It is known that bicyclo[2.2.1]heptene-2 (norbornene) and its substitution derivatives with short lateral chains can be polymerized by ring opening in the presence, as catalysts, of compounds of noble metals and a reducing substance such as an alcohol (see Michelotti U.S. Pat. No. 3,336,275; Michelotti et al "Co-ordinate polymerization of the bicyclo[2.2.1]heptene-2 Ring System (Norbornene) in Polar Media", Journal of Polymer Science, Part A, 3 (1965), pages 895-905; Rinehart U.S. Pat. No. 3,367,924 and Rinehart et al, "The emulsion polymerization of the Norbornene Ring System catalyzed by noble metal compounds", Polymer Letters 3 (1965), pages 1049-1052). Alternatively, such a polymerization can be achieved in the presence of a tungsten compound together with a compound having at least one metal-hydrocarbon link (see French Patent No. 1,599,185).
Also a polymer of this kind can be used as a main macromolecular constituent in the preparation of elastomer compositions by combining the polymer with at least one compound having a low volatility and a freezing point less than -30.degree. C., such as an ester or a mixture of hydrocarbons. This type of composition has been described by Vergne et al in U.S. Pat. No. 3,676,390 and in the above-cited French patent No. 1,599,185.
However, when bicyclo[ 2.2.1]heptene-2 or its substitution derivatives are polymerized using the known processes described above, there is obtained a compact mass which is more or less difficult to grind and to dry and more or less difficult to mix with compounds such as esters or hydrocarbons.